Water, Water Everywhere? · 2009-11-30 · 11Slide 11 Long Wavelengths May Contain a Thermal...
Transcript of Water, Water Everywhere? · 2009-11-30 · 11Slide 11 Long Wavelengths May Contain a Thermal...
Carle M. Pieters and the M3 TeamLEAG, November 16, 2009
Water, Water Everywhere?
Background:Water on the Moon
When samples werereturned from the Moon40 years ago, scientistsdiscovered…– The Earth and Moon share
an intimately intertwinedhistory, as well ascompositional links.
– The rocks of the Moon differfrom those of Earth:
• Lunar rocks are very oldand record early solarsystem processes.
• Lunar rocks are highlydepleted in volatiles.
We NOW know there are threeforms of LUNAR WATER:
2008: Lunar Interior– AE Saal et al. Nature 454, 192-195.
2009: Widespread Surficial– C Pieters (the M3 Team), R Clark (VIMS), J
Sunshine (the DI Team), Science, 326, 562-5722009: Polar Permanently Shadowed Region
– A Colaprete and the LCROSS Team
Our understanding of each of these new discoveries is in itsinfancy, but the scientific implications are enormous.
Water from the Lunar Interior
• Saal et al 2008, 2009: highprecision measurements ofvolcanic “green glass”
• The ancient lunar mantlecontained significantabundance of indigenouswater.– Best estimate: >700 ppm
(possibly higher)– Comparable to that of the
upper mantle of the modernEarth.
<= Core Rim =>
Water etc. atPolar Shadowed Regions
• Colaprete et al. andthe LCROSS Team,November 13, 2009
• Water and othervolatile componentswere excavatedfrom thepermanentlyshadowed “coldtraps” at the S Pole.
WidespreadSurficial Water
seen by theMoon Mineralogy
Mapper (M3)
R 2-µm absorption largely pyroxene
G Brightness
B 3-µm absorption OH/H2O
ISRO/NASA/JPL/Brown/USGS
7Slide 7
Moon Mineralogy Mapper (M3)on Chandrayaan-1
Chandrayaan-1 launchedOctober 22, 2008 on anIndian rocket
– Two-year mission planned– 100 km circular polar Orbit [200 km orbit May -
August 2009]
M3 is a NASA Discovery“Mission of Opportunity”
– Peer-reviewed competitive selection– Team led by PI: C. Pieters– Designed and built at JPL
M3 is a pushbroom imagingspectrometer
Two spatial dimensionsOne spectral dimension
260 Band260 BandSpectrumSpectrum
M3 covers the spectral rangewhere diagnostic features occurfor all common rock-formingminerals and hydrous phases[0.43 to 3.0 µm].
8Slide 8
M3 Is Designed toMeasure Mineralogy
Diagnosticabsorption bands ofiron-bearingminerals:• Olivine• Pyroxenes ofdifferent composition• Anorthosite
Soils exhibit asmooth continuumand much weakerabsorption bands.
0
0.2
0.4
0.6
0.8
500 1000 1500 2000 2500 3000
Re
fle
cta
nce
Wavelength (nm)
Olivine
Plagioclase
Pyroxenes
Soil
Spinel
M3 Resolution High Low
M3 provides compositional information about the surface at the highestspatial resolution possible with remote sensors.
9Slide 9
M3 and Chandrayaan-1Recent History
• M3 in-orbit operation and measurements were successful.– All instrument performance specifications were fully met.– Minimum Level 1 science requirements were nominally met: more
than 80% coverage in low-resolution Global Mode.– Remarkable science achievements: widespread surficial water;
lunar magma ocean confirmed; new rock types discovered, etc.
• From the beginning, the Chandrayaan-1 spacecraftsuffered technical difficulties and all operations were “non-nominal”.
• Communication with the spacecraft ceased prematurelyAugust 28, 2009.
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Example M3 spectra(from 182,000 in M3 image-cube)
•• NNArea ofArea ofspectrumspectrum
Wavelen
gth
Integrated Band Depth:Presence of mafic minerals
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Long Wavelengths May Contain aThermal Emission Component
R. N. Clark, 2009
If an addedcomponent isdiscernable, thetemperature is derivedfor each pixel of M3data. Emission isestimated andremoved.
Temperaturereflects solarirradiance andsurface albedo(mare vshighlands.
Clark et al., 2009
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Spectroscopy of LunarMinerals and H2O/OH
M3 R: 1580 nm AlbedoG: 1-µm IntegratedBand DepthB: 2-µm IntegratedBand Depth - TR
This display issensitive to thepresence anddiversity of maficminerals.
Isaacson et al. 2009
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0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
1800 2000 2200 2400 2600 2800 3000
Lat 81.7 scLat 76.6 scLat 67.1 scLat 43.2 scLat 23.0 scLat 18.0 sc
Scale
d R
eflecta
nce
Wavelength (nm)
m3g20090205t150614Eq Long 0.6 degBeta angle 50 deg
Spectroscopy of LunarSurface (M3) and H2O/OH
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Spatial Distribution
3-µm Hydroxyl &
18Slide 18
M3 data near 3-µm have beenthoroughly scrutinized.
• Repeat measurements– orbit-to-orbit overlap– Morning vs afternoon illumination– Before/after detector decontamination
• Independent M3 calibrations (spectralon, infragold, in-flight)
• 3-µm absorption band identified and extended to longerwavelengths by two independent spacecraft:– VIMS/Cassini (Clark, 2009)– Deep Impact (Sunshine et al., 2009)
In all cases the 3-µm absorption remained present.
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Independent Validationof M3 Results
VIMS Cassini 1999 fly by(reanalyzed by Clark, 2009)
Deep Impact June 2009 LunarFly-by (Sunshine et al. 2009)
Lunar Soil
Samples
DI Data
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M3 Maps Spatial Distribution
Ryder Crater[~17 km]on southernfarside
Relative 3-µmband depth
Diffuse relationwith illumination
M3
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Small Very Fresh HighlandCraters Exhibit Strong Bands
Arrows indicate the location of smallmorphologically fresh craters andtheir M3 near-infrared apparentreflectance spectra on the right.
The average spectrum forbackground soil (dashed line) isshown for comparison.
The small fresh feldspathic cratersexhibit prominent 3-µmabsorptions in comparison totheir surroundings.
[No detectible thermal component ]
M3
Relative Strength of the3-µm Absorption
Goldschmidt
Note: We cannot saywhether the absorptionoccurs at lower latitudeswithout additionalmeasurements at a lowertemperature.
LP Neutron Spectrometer D. Lawrence, 2006, 2009
The difference between LP-NS and M3 results suggests the twoinstruments are measuring water at different depths of the regolith, andimplies M3 detection of OH/H2O is surficial. LP analyses are ongoing……
Goldschmidt
PolarView
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Options for the Physical State ofObserved OH/H2O for Lunar Soils
• A few mono-layers of OH/H2Omolecules are formed across theuppermost surface that has access tothe solar wind.
• A small amount of OH/H2O thatoriginated on the surface is mixed intothe upper regolith.
• Hydrated minerals exist throughoutseveral millimeters of lunar regolith.
•Hydrated minerals form and are retained only in theuppermost surface of the regolith.•The upper few regolith grains are desiccated, butOH/H2O –bearing minerals are present just belowthe dry zone.
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Strength of the 3-µm Absorption Appearsto be Associated with Illumination
[ie, is Time Varying!]
• The most strongly illuminatedregion often exhibits theweakest OH/H2O absorptionbands.
• Observations may depend on:solar radiation intensity,temperature, geometry,surface composition, solarwind fluence, etc.
• Need to explore the physics ofthe interaction between asilicate body and the solarsystem environment.
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Summary: Composition of theMoon as Seen by M3
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Implications forPlanetary Exploration
1. The surficial OH/H2O identified by M3 may providea source for volatile accumulation elsewhere– In polar cold traps– Important implications for other airless bodies: Mercury,
asteroids, etc.2. Soils themselves may be a valuable resource.
More detailed measurements and laboratoryanalyses are needed to better constrain:– Bulk abundance of OH/H2O and spatial affinities– Processes responsible for formation & time-scale
involved3. Variability and rejuvenation should be priority
remote measurements.
2008: Lunar Interior– AE Saal et al. Nature 454, 192-195.
2009: Widespread Surficial OH/H2O– C Pieters (the M3 Team), R Clark (VIMS), J Sunshine (the DIR Clark (VIMS), J Sunshine (the DI
Team), Team), ScienceScience, 326, 562-572, 326, 562-572
2009: Polar Shadowed RegionShadowed Region–– A A Colaprete Colaprete and the LCROSS Teamand the LCROSS Team
Our understanding of each of these newthese newdiscoveries is in its infancy, but the scientificdiscoveries is in its infancy, but the scientificimplications are enormousimplications are enormous
We NOW know there are threeforms of LUNAR WATER:
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Back up
M3 Low-ResolutionCumulativeCoverage
Farside
100 km
+ 200 km Estimate
Nearside
OP1bRepeat
OP2a
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PDS Delivery of M3 Data
• Level 1b (Radiance at sensor; lunarselenographic location of each pixel):– OP1: June 2010– OP2 (blind): December 2010
• Level 2 (Apparent reflectance: solar,photometric, ground truth calibration):June 2011
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Cumulative M3 Data[The Sad Story]
Mission Period Baseline Low Res Baseline Hi Res
expectation
Actual Low Re s Actual Hi Re s
OP1 Nov 18, 2008 – Feb 14, 2009
Global coverage during high sun (± 30°) with cool detector
Test data, then begin prime target measurements
~30% coverage at low sun (45- 60°); 100 km orbit
One test ima g e
OP2 April 15 – Aug 16, 2009
Accumulate 15% science coverage during high sun (± 30°) with cool detecto r
~25% coverage at low sun (50- 60°), some redundant; 200 km orbit change, ~45% discontinuous coverag e
Test data at different conditio n s
OP3
[Nov 1 – Jan 31, 2010]
Accumulate additional 15% science covera g e
OP4 [May 1 – July 31, 2010 ]
Accumulate additional 15% science covera g e
Total >90% contiguous
coverage at high sun [Basema p ]
30-45% coverage of prime science targets
~90% discontinuous coverage, at low sun, different altitudes
Test data
Low Resolution Mode (Global): 140 m/pixel, 85 spectral channels (0.4 – 3.0 !m) at 100 km High Resolutio Mode (Target): 70 m/pixel, 260 spectral channels (0.4 – 3.0 !m) at 100 km [x12 improvement]
Low Sun: Great for Morphology!Low Sun: Great for Morphology!
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Low Sun =Low Signal and Shadows
Low Sun:Not good forspectroscopy!
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Low- and High-ResolutionComparison
The few high resolution targets M3
acquired did not cover new, excitingdiscoveries (i.e., unshockedanorthosite, OH/H2O, spinel); theywere rather test targeted dataacquired only when missionoperations allowed (near the end ofoperations).
Target: Full Res
Global
Low Res
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M3 Provideda Taste of What Is Possible
• The ISRO Operations and Flight Teams performedmagnificently in a constantly challenging environment.Through their hard work and creative efforts, M3
accumulated data to meet minimum Level 1 Sciencerequirement (>80% low-resolution coverage).
• Unfortunately, although M3 met every designrequirement,– None of the baseline expectations were achieved (high sun,
basemap, science targets assessment);– The intended design and performance capabilities of M3 were
not utilized (higher spatial and spectral resolution x 12);– There is currently no opportunity to follow-up on the important
discoveries identified in M3 low-resolution data.